Method of preparing low-temperature-cure polymer composition

ABSTRACT

A method of preparing a composition containing a fluorocarbon thermoplastic random copolymer comprising the steps of: 
     (A) providing a mixture having: 
     (i) a fluorocarbon thermoplastic random copolymer having subunits of: 
     
       
         —(CH 2 CF 2 )x—, —(CF 2 CF(CF 3 )y—, and —(CF 2  CF 2 )z—, 
       
     
      wherein 
     x is from 1 to 50 or 60 to 80 mole percent, 
     y is from 10 to 90 mole percent, 
     z is from 10 to 90 mole percent, 
     x+y+z equals 100 mole percent; 
     (ii) a filler comprising zinc oxide; 
     (iii) a curable amino functional polydimethyl siloxane copolymer comprising aminofunctional units selected from the group consisting of (aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl) dimethyl; and 
     (iv) antimony-doped tin oxide particles; 
     (v) a bisphenol residue curing agent; and 
     (B) curing the mixture for 5 to 10 hours at a temperature in the range of 25° C. to 275° C.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly assigned, copending U.S. patentapplication Ser. Nos.:

Ser. No. 09/609,562 by Chen et al., now U.S. Pat. No. 6,355,354, filedof even date herewith, entitled “FLUOROCARBON THERMOPLASTIC RANDOMCOPOLYMER COMPOSITION CURABLE AT LOW TEMPERATURES”;

Ser. No. 09/608,362 by Chen et al., filed of even date herewith,entitled “FUSER MEMBER WITH LOW-TEMPERATURE-CURE OVERCOAT”;

Ser. No. 09/608,818 by Chen et al., filed of even date herewith,entitled “METHOD OF CURING A FUSER MEMBER OVERCOAT AT LOW TEMPERATURES”.

FIELD OF THE INVENTION

This invention relates to a method of preparing compositions containinga fluorocarbon thermoplastic random copolymer. More particularly, theinvention relates to a method of preparing compositions containing afluorocarbon thermoplastic random copolymer, zinc oxide, anaminosiloxane, and antimony-doped tin oxide particles. Such compositionsare capable of being cured at lower temperatures compared withconventional fluorocarbon polymer compositions and are useful ascoatings, sheets, or films where high temperature resistance isrequired.

BACKGROUND OF THE INVENTION

Fluororesins, including both fluorocarbon elastomers and fluorocarbonthermoplastics, are widely used in the form of sheet, film, coatings andlaminates in various fields due to their characteristic properties suchas good heat resistance, good chemical resistance and good weatherresistance. These materials find applications as gaskets and seals inautomotive fuel delivery, engine, and powertrain systems, tank and pipeliners, release layers on compression molds, layers onelectrophotographic toner fuser rollers or belts, valve stem androtating shaft sealant coatings, roller and bearing coatings, andsealants for porous materials such as ceramics and fabric, for example.In addition to their characteristic resistance to heat, chemicals, andweather, and depending upon the particular application these fluororesincompositions may also need to provide appropriate frictionalcharacteristics, abrasion and wear resistance, flexibility,processability, and adhesion to a particular substrate.

Polyfluorocarbon elastomers, such as vinylidenefluoride-hexafluoropropylene copolymers, are tough, wear resistant andflexible elastomers that have excellent high temperature resistance, butrelatively high surface A energies, which compromise applications whererelease properties are critical, for example as release layers oncompression molds or outer layers on electrophotographic toner fusermembers.

Fluorocarbon resins like polytetrafluoroethylene (PTFE) or fluorinatedethylenepropylene (FEP) are fluorocarbon thermoplastics which haveexcellent release characteristics due to very low surface energy.Fluorocarbon thermoplastic resins are, however, less flexible andelastic than fluorocarbon elastomers and often require high temperaturecuring for long time periods to sinter the polymer into a continuous anduseful layer or sheet.

Both fluorocarbon elastomers and fluorocarbon thermplastics have beenused to prepare high temperature resistant surfaces. For example, U.S.Pat. No. 4,999,221 describes a process for powder coating a substratewith a fluoroplastic material to provide a heat resistant surface layer.U.S. Pat. Nos. 5,919,886 and 6,020,450 describe a room temperaturecurable fluoropolymer composition containing an organosilicon compoundand a condensation accelerator having improved heat resistance andweatherability.

U.S. Pat. Nos. 5,948,479 and 6,068,931 describe composite materials forself-lubricating slide bearings containing a fluorothermoplasticcomposite overlayer on a porous metal bearing.

Fluororesin-containing compositions have also been successfully employedin various electrostatographic applications. For example, U.S. Pat. Nos.4,568,275 and 5,599,631 disclose a fuser roll having a layer offluorocarbon elastomer and a fluorinated resin powder. However, thefluorocarbon resin tends to phase separate from the fluorocarbonelastomer thereby diminishing performance.

U.S. Pat. No. 4,853,737 discloses a fuser roll having an outer layercomprising cured fluorocarbon elastomers containing pendant aminefunctional polydimethylsiloxane that are covalently bonded to thebackbone of the fluorocarbon elastomer. However, the amine functionalpolydimethylsiloxane tends to phase separate from the fluorocarbonelastomer.

U.S. Pat. No. 5,582,917 discloses a fuser roll having a surface layercomprising a fluorocarbon-silicone polymeric composition obtained byheating a fluorocarbon elastomer with a fluorocarbon elastomer curingagent in the presence of a curable polyfunctional poly(C1-6 alkyl)siloxane polymer. However, the resulting interpentrating network (IPN)has relatively high coefficient of friction and relatively lowmechanical strength. After a period of use, the release property of theroller degrades and paper jams begin to occur.

U.S. Pat. No. 5,547,759 discloses a fuser roll having a release coatinglayer comprising an outermost layer of fluorocarbon resin uniquelybonded to a fluoroelastomer layer by means of a fluoropolymer containinga polyamide-imide primer layer. Although the release coating layer hasrelatively low surface energy and good mechanical strength, the releasecoating layer lacks flexibility and elastic properties and can notproduce high quality of images. In addition, sintering the fluorocarbonresin layer is usually accomplished by heating the coated fuser memberto temperatures of approximately 350° C. to 400° C. Such hightemperatures can have a detrimental effect on the substrate to which thefluorocarbon resin has been applied, especially, for example, if thesubstrate is a polymeric material. It would be desirable to provide afluorocarbon composition that can be formed and/or cured withoutdamaging the substrate to which it has been applied.

U.S. Pat. No. 5,595,823 discloses toner fusing members which have asubstrate coated with a fluorocarbon random copolymer containingaluminum oxide. Although these toner fusing members have provedeffective and have desirable thermal conductivity, they have a problemin that there can be toner contamination. The advantage of using thecured fluorocarbon thermoplastic random copolymer compositions is thatthey are effective for use with toner release agents which typicallyinclude silicone.

U.S. Pat. No. 6,035,780 describes a process to prepare a compatibilizedblend of a fluoroelastomer and a polysiloxane useful forelectrostatographic and liquid ink printing machine applications. Thecompatible blend is reportedly useful as a component of long-life fuserrolls, backing rolls, transfer and transfuse belts and rolls and biascharging and biastransfer rolls.

U.S. Pat. No. 5,464,698 discloses toner fusing members which have asubstrate coated with a fluorocarbon random copolymer containing tinoxide. Although these toner fusing members have proved effective andhave desirable thermal conductivity, they have a problem in that therecan be toner contamination.

Commonly-assigned U.S. Pat. No. 6,041,210 describes a toner fusingmember having an overcoat layer including electrically conductive finepowders having a weight percent between about 30 to 80 weight percent.Although these toner fusing members have proved effective in suppressingelectrostatic charge build up, they have a problem in that there can betoner contamination.

As evidenced by the above description, fluororesin compositions havebeen widely utilized in a variety of critical applications requiringresistance to severe or aggressive environments, abrasion and wearresistance, surface lubricity, and release properties. However, it hasbeen extremely difficult to provide a fluororesin composition whichsimultaneously provides most or all of these characteristics and can becured at temperatures as low as room temperature. It is toward asolution to this problem that the present invention is directed.

SUMMARY OF THE INVENTION

The present invention provides a method of preparing a compositioncontaining a fluorocarbon thermoplastic random copolymer that is easilyprocessed into a coating or sheet having improved release properties,surface lubricity, mechanical strength, and low curing temperatures. Themethod comprises the steps of:

(A) providing a mixture having:

(i) a fluorocarbon thermoplastic random copolymer having subunits of:

—(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and —(CF₂CF₂)z—,

 wherein

x is from 1 to 50 or 60 to 80 mole percent,

y is from 10 to 90 mole percent,

z is from 10 to 90 mole percent,

x+y+z equals 100 mole percent;

(ii) a filler comprising zinc oxide;

(iii) a curable amino functional polydimethyl siloxane copolymercomprising aminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl; and

(iv) antimony-doped tin oxide particles;

(v) a bisphenol residue curing agent; and

(B) curing the mixture for 5 to 10 hours at a temperature in the rangeof 25° C. to 275° C.

The compositions prepared as described above are suitable for use as acoating on a variety of substrates or as a free standing slab or film.The coatings may be applied to substrates such as metals, polymers,ceramics, or glass. The substrate may be in essentially any form orshape, for example, a sheet, a web, a roller, a machined part, etc. Whenapplied to a substrate, the compositions are coated from an organicsolvent, then dried at ambient or elevated temperature, and then curedas described above. Hence, the invention also provides a method ofpreparing a coating composition for a substrate comprising the steps of:

(A) providing a composition having:

(i) a fluorocarbon thermoplastic random copolymer having subunits of:

(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and —(CF₂CF₂)z—,

 wherein

x is from 1 to 50 or 60 to 80 mole percent,

y is from 10 to 90 mole percent,

z is from 10 to 90 mole percent,

x+y+z equals 100 mole percent;

(ii) a filler comprising zinc oxide;

(iii) a curable amino functional polydimethyl siloxane copolymer

 comprising aminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl)

methyl and (aminopropyl) dimethyl; and

(iv) antimony-doped tin oxide particles; and

(v) a bisphenol residue curing agent;

(3) providing a substrate;

(C) coating the substrate with the composition in an organic medium;

(D) allowing the composition to dry on the substrate at ambient or

 elevated temperatures; and

(E) curing the composition for 5 to 10 hours at a temperature in the

 range of 25° C. to 275° C.

The composition may also be cured for 5 to 10 hours at a temperature inthe range of 25° C. to 120° C. Alternatively, the composition may becured for 5 to 10 hours at a temperature in the range of 25° C. to 50°C. Preferably, the composition is cured for 5-10 hours a temperature ofabout 25° C.

The aminosiloxane is an amino functional polydimethyl siloxane copolymercomprising aminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl.

Optionally, the composition of the invention may further contain afluorinated resin selected from the group of polytetrafluoroethylene orfluoroethylenepropylene having a number average molecular weight ofbetween 50,000 and 50,000,000. The composition may further containcarbon black.

As will be demonstrated through examples, compositions comprising anunfilled fluorocarbon thermoplastic random copolymer have poormechanical properties. However, it has been surprisingly found in thepresent invention that a fluorocarbon thermoplastic random copolymercontaining zinc oxide filler, an aminosiloxane polymer, and a bisphenolresidue curing agent provides a composition having improved mechanicalproperties. It was particularly surprising that the addition ofantimony-doped tin oxide particles to these compositions significantlyreduced the temperatures required for curing.

A further advantage of the present invention is that the addition ofspecific release additives such as fluorinated resins significantlyimproves the frictional characteristics of the fluorocarbonthermoplastic random copolymer- containing compositions.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

The compositions of the invention contain a fluorocarbon thermoplasticrandom copolymer that is cured by a curing agent. The fluorocarbonrandom copolymer has subunits of:

—(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and —(CF₂CF₂)z—,

wherein

x is from 1 to 50 or 60 to 80 mole percent,

y is from 10 to 90 mole percent,

z is from 10 to 90 mole percent,

x+y+z equal 100 mole percent.

—(CH₂CF₂) is (vinylidene fluoride subunit (“VF₂”)),

—(CF₂CF(CF₃) is (hexafluoropropylene subunit (“FP”)), and

—(CF₂CF₂) is (tetrafluoroethylene subunit (“TFE”)).

The curing agent has a bisphenol residue. By the term bisphenol residueis meant bisphenol or a derivative such as bisphenol AF.

The composition further includes a particulate filler having zinc oxide,an aminosiloxane, and antimony-doped tin oxide particles.

The aminosiloxane is an amino functional polydimethyl siloxane copolymercomprising aminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl.

In these formulas, x, y, and z are mole percentages of the individualsubunits relative to a total of the three subunits (x+y+z), referred toherein as “subunit mole percentages”. The curing agent can be consideredto provide an additional “cure-site subunit”, however, the contributionof these cure-site subunits is not considered in subunit molepercentages. In the fluorocarbon thermoplastic copolymer, x has asubunit mole percentage of from 1 to 50 or 60 to 80 mole percent, y hasa subunit mole percentage of from 10 to 90 mole percent, and z has asubunit mole percentage of from 10 to 90 mole percent. In a currentlypreferred embodiment of the invention, subunit mole percentages are: xis from 30 to 50 or 70 to 80, y is from 10 to 20, and z is from 10 to50; or more preferably x is from 40 to 50, y is from 10 to 15, and z is40 to 50. In the currently preferred embodiments of the invention, x, y,and z are selected such that fluorine atoms represent at least 65percent of the total formula weight of the VF₂, HFP, and TFE subunits.

A curable amino functional polydimethyl siloxane copolymer is used inthe present invention and is cured with the fluorocarbon thermoplasticrandom copolymer to produce a material suitable for use in a variety ofapplications including seals and gaskets, heat resistant coatings forbelts, rollers, and bearings, release layers for compression molds andelectrostatographic fuser members, etc.

An optional release additive such as a fluorinated resin can be added tothe fluorocarbon thermoplastic random copolymer-containing compositionsto further improve the surface lubricity of the compositions.

The conditions employed for curing are largely determined by theparticular application for the cured fluorocarbon thermoplastic randomcopolymer-containing composition. For example, when the compositions areprepared as a slab or free standing film, higher temperatures and longercuring times may be employed. When the compositions are applied as acoating on a substrate, particularly polymeric substrates, lower curingtemperatures and shorter curing times may be more appropriate. In apreferred embodiment, the substrate is either a metal or a ceramic, andthe fluorocarbon thermoplastic random copolymer-containing mixtures arecured for 5-10 hours at a temperature of 25° C. to 275° C. In anotherpreferred embodiment, the substrate is either a metal or a ceramic, andthe fluorocarbon thermoplastic random copolymer-containing mixtures arecured for 5-10 hours at a temperature of 25 to 120° C. In a yet anotherpreferred embodiment, the substrate is either a plastics or apolyyrethane, and the fluorocarbon thermoplastic randomcopolymer-containing mixtures are cured for about 5-10 hours at atemperature of about 25° C.

A preferred class of curable amino functional polydimethyl siloxanes,based on availability, includes those having functional groups such asaminopropyl or aminoethylaminopropyl pendant from the siloxane backbonesuch as DMS-A11, DMS-A12, DMS-A15, DMS-A21 and DMS-A32 (sold by Gelest,Inc.) having a number average molecular weight between 850 and 27,000.Particularly preferred curable amino functional polydimethyl siloxanesare bis(aminopropyl) terminated poly(dimethylsiloxane). Such oligomersare available in a series of molecular weights as disclosed, forexample, by Yilgor et al., “Segmented Organosiloxane Copolymer”,Polymer,1984, V.25, ppl1800-1806. Other curable amino functionalpolydimethyl siloxanes which can be used are disclosed in U.S. Pat. Nos.4,853,737 and 5,157,445, the disclosures of which are herebyincorporated by reference.

Preferred compositions of the invention have a ratio of aminosiloxanepolymer to fluorocarbon thermoplastic random copolymer between about0.01 and 0.2 to 1 by weight, preferably between about 0.05 and 0.15to 1. The composition is preferably obtained by curing a mixturecomprising from about 50-80 weight percent of a fluorocarbonthermoplastic copolymer, 5-20 weight percent, most preferably about 5-10weight percent, of a curable amino functional polydimethyl siloxanecopolymer, 1-5 weight percent of a bisphenol residue, 1-20 weightpercent of a zinc oxide acid acceptor type filler, 3-20 weight percentof antimony-doped tin oxide particles, 0 to 10 weight percent of carbonblack, and 10-50 weight percent of a fluorinated resin.

The compositions of the invention include a particulate fillercomprising zinc oxide. The zinc oxide particles can be obtained from aconvenient commercial source, e.g., Atlantic Equipment Engineers ofBergenfield, N.J. In a currently preferred embodiment, the particulatezinc oxide filler has a total concentration in the compositions of theinvention of from about 1 to 20 parts per hundred parts by weight of thefluorocarbon thermoplastic random copolymer (pph). Concentrations ofzinc oxide much greater than 20 parts by weight will render thecomposition to stiff. In a particular embodiment of the invention, thecomposition has 3 to 15 pph of zinc oxide.

The particle size of the zinc oxide filler does not appear to becritical. Particle sizes anywhere in the range of 0.1 to 100 micrometershave been found to be acceptable. In the examples presented below thezinc oxide particles were from 1 to 40 micrometers in diameter.

The compositions of the invention also include antimony-doped tin oxideparticles. These particles can be obtained from a convenient commercialsource, e.g., Keeling & Walker, Stoke-on-Trent, UK; DuPont Co; orMitsubishi Metals Inc., Japan. In a currently preferred embodiment, theantimony-doped tin oxide particles have a total concentration in thecompositions of the invention of from about 3 to 20 parts per hundredparts by weight of the fluorocarbon thermoplastic random copolymer(pph). In a particularly preferred embodiment of the invention, thecomposition has 3 to 15 pph of antimony-doped tin oxide particles.

The particle size of the antimony-doped tin oxide particles does notappear to be critical. Particle sizes anywhere in the range of 0.05 to10 micrometers are suitable. In the examples presented below the tinoxide particles were about 0.4 micrometers in diameter. The morphologyor shape of the particles is not critical, for example, the particlesmay be essentially spherically in shape (granular) or they may beacicular in shape (e.g., a fiber or whisker)

The antimony concentration of the antimony-doped tin oxide particles ispreferably 1 to 15 weight percent, most preferably 3 to 10 weightpercent. In the examples presented below the antimony-doped tin oxideparticles contained 6 to 9 weight percent antimony.

It was surprisingly found that the addition of the antimony-doped tinoxide particles to the fluorocarbon thermoplastic random copolymercompositions greatly reduced the temperatures needed to cure thefluoropolymer. While not wanting to be bound by theory, it is possiblethat the antimony acts as a catalyst for the curing reactions.Conventional fluoropolymer compositions that do not containantimony-doped tin oxide parties have curing temperatures that aretypically about 220 to 280° C., while the compositions of the inventionmay be cured at temperatures as low as room temperature.

The compositions of the invention optionally contain a carbon blackadded at a concentration of 0 to 10 parts per hundred parts of thefluorocarbon thermoplastic random copolymer. Any conventional carbonblack may be used, for example Thermax™ N-990 available from R.T.Vanderbilt Co.

To prepare the compositions of the invention, the zinc oxide particlesand antimony-doped tin oxide particles are mixed with the uncuredfluorocarbon thermoplastic random copolymer, aminosiloxane, a bisphenolresidue curing agent, and any other additives, such as fluorinated resinand carbon black, and cured. The fluorocarbon thermoplastic randomcopolymer is cured by crosslinking with basic nucleophile additioncuring. Basic nucleophilic cure systems are well known and arediscussed, for example, in U.S. Pat. No. 4,272,179. One example of sucha cure system combines a bisphenol as the curing agent and anorganophosphonium salt, as an accelerator. The fluorinated resins whichinclude polyterafluoroethylene (PTFE) or fluoethylenepropylene (FEP) arecommerically available from Dupont.

The curing agent is incorporated into the polymer as a cure-sitesubunit, for example, bisphenol residues. Other examples of nucleophilicaddition cure systems are sold commercially as DLIK No. I(hexamethylenediamine carbamate) and DIAK No. 3(N,N′-dicinnamylidene-1,6-hexanediamine) by Dupont.

Suitable fluorocarbon thermoplastic random copolymers are availablecommercially. In a particular embodiment of the invention, a vinylidenefluoride-co-tetrafluoroethylene co-hexafluoropropylene was used whichcan be represented as —(VF)(75)—(TFE) (10)—(HFP)(25)—. This material ismarketed by Hoechst Company under the designation “THV Fluoroplastics”and is referred to herein as “THV”. In another embodiment of theinvention, a vinylidenefluoride-co-tetrafluoroethylene-co-hexafluoropropylene was used whichcan be represented as —(VF)(49)—(TFE) (41)—(HFP)(10)—. This material ismarketed by Minnesota Mining and Manufacturing, St. Paul, Minn., underthe designation “3M THV” and is referred to herein as “THV-200A”. Othersuitable uncured vinylidene fluoride-cohexafluoropropylenes andvinylidene fluoride-co-tetrafluoroethylene-cohexafluoropropylenes areavailable, for example, THV-400, THV-500 and THV-300.

In general, THV Fluoroplastics are set apart from other melt-processablefluoroplastics by a combination of high flexibility and low processtemperatures. With flexural modulus values between 83 Mpa and 207 Mpa,THV Fluoroplastics are the most flexible of the fluoroplastics.

The molecular weight of the uncured polymer is largely a matter ofconvenience, however, an excessively large or excessively smallmolecular weight would create problems, the nature of which are wellknown to those skilled in the art. In a preferred embodiment of theinvention the uncured polymer has a number average molecular weight inthe range of about 100,000 to 200,000.

Curing of the fluorocarbon thermoplastic random copolymer is carried outat much lower temperatures compared to the well known conditions forcuring vinylidene fluoride based fluorocarbon elastomer copolymers. Forexample, the cure of fluorocarbon elastomers is usually for 12-48 hoursat temperatures of about 220 to 250° C. Typically, fluorocarbonelastomer coating compositions are dried until solvent free at roomtemperature, then gradually heated to about 230° C. over 24 hours, thenmaintained at that temperature for 24 hours. By contrast, the cure ofthe fluorocarbon thermoplastic random copolymer compositions of thecurrent invention is about 5 to 10 hours at a temperature of about25-275° C., preferably 25-120° C., and most preferably 25-50° C.

In the practice of the present invention, a method of preparing acomposition containing a fluorocarbon thermoplastic random copolymercomprises the steps of:

(a) providing a mixture having:

(i) a fluorocarbon thermoplastic random copolymer having subunits of:

—(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and —(CF₂CF₂)z—,

 wherein

x is from 1 to 50 or 60 to 80 mole percent,

y is from 10 to 90 mole percent,

z is from 10 to 90 mole percent,

x+y+z equals 100 mole percent;

(ii) a filler comprising zinc oxide;

(iii) a curable amino functional polydimethyl siloxane copolymercomprising aminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl; and

(iv) antimony-doped tin oxide particles;

(v) a bisphenol residue curing agent;

(b) curing the mixture for 5-10 hours at a temperature in the range of25° C. to 275° C.

The compositions prepared as described above are suitable for use as acoating on a variety of substrates or as a free standing slab or film.The coatings may be applied to substrates such as metals, polymers,ceramics, or glass. The substrate may be in essentially any form orshape, for example, a sheet, a web, a roller, a machined part, etc.

The invention is further illustrated by the following Examples andComparative Example.

EXAMPLES 1-3

150 grams of Fluorocarbon thermoplastic random copolymer THV 200A, 1.05grams of zinc oxide, 15.4 grams of fluorinated resin, and 4.90 grams ofaminosiloxane were mixed into 230 grams of methyl ethyl ketone in amilling crock as indicated (amounts listed as parts per hundred parts ofTHV200A) in Table 1. THV200A is a commercially available fluorocarbonthermoplastic random copolymer which is sold by 3M Corporation. The zincoxide particles can be obtained from convenient commercial source, e.g.,Atlantic Equipment Engineers of Bergenfield, N.J. The amino siloxaneDMS-A21 is commercially available from Gelest, Inc. The fluorinatedresin is fluoroethylenepropylene (FEP) and is commercially availablefrom Dupont. Into the above mixture antimony-doped tin oxide particlesand carbon black were added and the formulations were mixed on atwo-roll mill for 48 hours to form a dispersion (the amounts of theantimony-doped tin oxide particles and carbon black are given in Table1). The antimony-doped tin oxide particles are Keeling & Walker Inc.CPM375 having an average particle size of about 0.4 μm and an antimonycontent of 6-9 weight %. The carbon black is Thermax™ N-990 availablefrom R. T.Vanderbilt Co.

Each of the above dispersions were mixed with 1.05 grams (3 pph) ofcurative 50 (a bisphenol residue, DuPont)and roll milled for 2-3minutes. The dispersions were then immediately cast into a film andallowed to dry for several hours. The resulting films had a thickness ofseveral mils. Afterwards the cast films were cured using the conditionslisted in Table 2.

COMPARATIVE EXAMPLE 1

To prepare Comparative Example 1 substantially the same procedures werefollowed as in Example 1-3, with the following exception. As indicatedin the composition listed in Table 1, Comparative Example 1 did notcontain antimony-doped tin oxide or carbon black. The curing conditionsemployed are given in Table 2.

TABLE 1 Amino- CMP375 Carbon Sample THV 200A ZnO siloxane FEP Tin oxideblack Example 1 100 3 14 44 8 2 Example 2 100 3 14 44 8 0 Example 3 1003 14 44 8 2 Comparative 100 3 14 44 0 0 Example 1

TABLE 2 Max. Temp. Sample Post Cured For Curing Example 1 No 25° C.Example 2 No 25° C. Example 3 Yes 275° C.  Comparative No 25° C. Example1

DMA: Testing Method

The samples were tested on a Rheometrics RSA II Dynamic MechanicalAnalyzer (DMA) and required a sample geometry of 7.5 mm×23 mm with athickness between 30 microns to 2000 microns. The free standing filmswere tested at 10Hz and a strain of 0.07%. The test was recorded over atemperature scan of −100° C. to 200° C. Over the temperature scan anoscillatory strain is applied to the sample and the resulting stress ismeasured. These values are related to material properties by E′ and E″(Storage and Loss Moduli, respectively). As a result of DMA testing, thestorage modulus (E′) at three different temperatures is determined andthe behavior of the material at high temperature is observed.

TABLE 3 Storage Modulus Versus Temperature Sample MPa @ 80° C. MPa @140° C. MPa @ 175° C. Example 1 28.0 7.05 7.05 Example 2 20.0 4.50 4.50Example 3 11.5 4.8 4.8 Comparative 11.0 0.9 0.3 Example 1

Table 3 shows a comparison between the cured fluorocarbon thermoplasticrandom copolymer compositions of the invention and Comparative Example 1which did not contain antimony-doped tin oxide. The comparative example,despite containing the bisphenol residue curing agent, did not cure atlow temperature because it did not contain the antimony-doped tin oxidewhich apparently acts as an accelerator for curing. In terms of themodulus at 175° C., the cured fluorocarbon thermoplastic randomcopolymer compositions of the invention provide a significantimprovement in mechanical properties at the high temperature. Also, thecompositions of the invention can also be cured at conventional hightemperatures as in Example 3 without any significant deleterious effecton properties.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof, but it should be appreciated thatvariations and modifications can be effected within the scope of theinvention.

What is claimed is:
 1. A method of preparing a composition containing afluorocarbon thermoplastic random copolymer comprising the steps of: (A)providing a mixture having: (i) a fluorocarbon thermoplastic randomcopolymer having subunits of: —(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and—(CF₂CF₂)z—,  wherein x is from 1 to 50 or 60 to 80 mole percent, y isfrom 10 to 90 mole percent, z is from 10 to 90 mole percent, x +y+zequals 100 mole percent; (ii) a filler comprising zinc oxide; (iii) acurable amino functional polydimethyl siloxane copolymer comprisingaminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl; and (iv) antimony-doped tin oxide particles; (v) a bisphenolresidue curing agent; and (B) curing the mixture for 5 to 10 hours at atemperature in the range of 25° C. to 275° C.
 2. The method of claim 1wherein the aminosiloxane is an amino functional polydimethyl siloxanecopolymer.
 3. The method of claim 2 wherein the amino functionalpolydimethyl siloxane copolymer comprises amino functional unitsselected from the group consisting of (aminoethylaminopropyl) methyl,(aminopropyl) methyl and (aminopropyl) dimethyl.
 4. The method of claim1 wherein the amino siloxane has a total concentration of from 1 to 20parts by weight per 100 parts of the fluorocarbon thermoplastic randomcopolymer.
 5. The method of claim 1 wherein the zinc oxide has a totalconcentration of from 1 to 20 parts by weight per 100 parts of thefluorocarbon thermoplastic random copolymer.
 6. The method of claim 1wherein the zinc oxide has a total concentration in the layer of from 3to 15 parts by weight per 100 parts of the fluorocarbon thermoplasticrandom copolymer.
 7. The method of claim 1 wherein the fluorocarbonthermoplastic random copolymer is cured by bisphenol residues.
 8. Themethod of claim 1 wherein the fluorocarbon thermoplastic randomcopolymer is nucleophilic addition cured.
 9. The method of claim 1wherein x is from 30 to 50 mole percent, y is from 10 to 90 molepercent, and z is from 10 to 90 mole percent.
 10. The method of claim 1wherein x is from 40 to 50 mole percent and y is from 10 to 15 molepercent.
 11. The method of claim 1 wherein z is greater than 40 molepercent.
 12. The method of claim 1 wherein the antimony-doped tin oxideparticles have a total concentration of from 3 to 20 parts by weight per100 parts of the fluorocarbon thermoplastic random copolymer.
 13. Themethod of claim 1 wherein antimony-doped tin oxide particles comprise 3to 10 weight percent antimony.
 14. The method of claim 1 wherein thefluorocarbon thermoplastic random copolymer further comprises afluorinated resin.
 15. The method of claim 14 wherein the fluorinatedresin has a number average molecular weight of between 50,000 to50,000,000.
 16. The method of claim 14 wherein the fluorinated resin ispolytetrafluoroethylene or fluoroethylenepropylene.
 17. The method ofclaim 1 wherein the mixture is cured for 5 to 10 hours at a temperaturein the range of 25° C. to 275° C.
 18. The method of claim 1 wherein themixture is cured for 5 to 10 hours at a temperature in the range of 25°C. to 120° C.
 19. The method of claim 1 wherein the mixture is cured for10 hours at a temperature of about 25° C.
 20. A method of preparing acoating composition for a substrate comprising the steps of: a)providing a mixture having: i) a fluorocarbon thermoplastic randomcopolymer having subunits of: —(CH₂CF₂)x—, —(CF₂CF(CF₃)y—, and—(CF₂CF₂)z—,  wherein x is from 1 to 50 or 60 to 80 mole percent, y isfrom 10 to 90 mole percent, z is from 10 to 90 mole percent, x+y+zequals 100 mole percent; ii) a filler comprising zinc oxide; iii) acurable amino functional polydimethyl siloxane copolymer comprisingaminofunctional units selected from the group consisting of(aminoethylaminopropyl) methyl, (aminopropyl) methyl and (aminopropyl)dimethyl; and iv) and antimony-doped tin oxide; v) a bisphenol residuecuring agent; b) providing a substrate; c) coating the substrate withthe composition in an organic medium; d) allowing the composition to dryon the substrate at ambient or elevated temperatures; and e) curing thecomposition for 5 to 10 hours at a temperature in the range of 25° C. to275° C.